Fluid flow actuated device

ABSTRACT

A positive displacement fluid actuated device for measuring flow volume and flow rate of a fluid. The device has at least one cylinder containing a pressure wall means movable by fluid pressure through longitudinal working strokes in the cylinder, and a transducer for generating signals representing the linear velocity and/or position of the pressure wall means. A readout unit may be connected to the transducer for converting the signals to readouts representing flow rate and/or flow volume. One feature of the invention resides in the use of a roller and elastic band arrangement, commonly known as a ROLAMITE, for the pressure wall means. According to another feature, the fluid actuated device embodies a pair of cylinders, each of whose pressure wall means performs a valving function for controlling fluid flow to the other cylinder in such a way that the pressure wall means are driven through their working strokes alternately.

United States Patent [191 Rhoades I FLUID FLOW ACTUATED DEVICE [76] Inventor:

Rex V Rhoades, 2510 San Andres Way, Claremont, Calif. 91711 Primary Examiner-Herbert Goldstein Assistant ExaminerJohn P. Beauchamp Attorney, Agent, or FirmBoniard I. Brown Dec. 24, 1974 ABSTRACT A positive displacement fluid actuated device for measuring flow volume and flow rate of a fluid. The device has at least one cylinder containing a pressure wall means movable by fluid pressure through longitudinal working strokes in the cylinder, and a transducer for generating signals representing the linear velocity and- /or position of the pressure wall means. A readout unit may be connected to the transducer for converting the signals to readouts representing flow rate and/or flow volume. One feature of the invention resides in the use of a roller and elastic band arrangement, commonly known as a ROLAMlTE, for the pressure wall means. According to another feature, the fluid actuated device embodies a pair of cylinders, each of whose pressure wall means performs a valving function for controlling fluid flow to the other cylinder in such a way that the pressure wall means are driven through their working strokes alternately.

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CL USTER D/SPLA CEMENT FLUID FLOW ACTUATED DEVICE BACKGROUND OF THE INVENTION ment fluid actuated devices for measuring the flow volume and flow rate of a fluid.

2. Discussion of the Prior Art A wide variety of fluid flowmeters have been devised for measuring both flow volume, i.e'., total volume of fluid flowing through the flowmeter during the period of measurement, and flow rate, i.e., volume of fluid flowing through the flowmeter per unit of time. These existing flowmeters range from relatively simple to very sophisticated devices, the accuracy and precision of flow measurement increasing, as a general rule, with the degree of sophistication and hence cost.

The present invention provides a positive displacement fluid actuated device which, although very simple in construction and operation, is uniquely adapted to measure fluid flow volume and flow rate with a relatively high degree of accuracy and precision. According to one important aspect of the invention, these features of simplicity, accuracy and precision are achieved by utilization of a virtually frictionless roller mechanism known as a ROLAMITE as the flow metering means of the device.

Simply stated, a roller mechanism of this kind comprises a pair of cylindrical rollers movable through a guideway between two parallel guide surfaces. The rollers have diameters greater than one-half the spacing between the guide surfaces and have axes parallel to the guide surfaces. An elastically flexible band is attached at its ends to the guide surfaces, respectively, and is trained about the rollers in such a way that the band extends from one end of the guideway along in contact with one guide surface and between the latter and the adjacent roller, then around this roller and between the latter and the other roller, then around the latter roller and between it and the other guide surface, and finally along and in contact with the latter surface to the opposite end of the guideway. The rollers are movable through the guideway with virtually frictionless. pure rolling contact between the rollers and band.'

The two rollers and the portion of the band entwining the rollers is referred to as a roller cluster.

This virtually frictionless motion of the rollers constitutes one striking feature of the roller mechanism. Another unique and important feature resides in the fact that the flexible elastic band stores elastic strain energy which controls the driving force of the rollers. The band may be shaped, notched, slotted, or otherwise alteredto translate this strain energy into various forces on the rollers. For example, the band may be notched or chemically etched to define an area of reduced thickness to provide the band with a negative spring ac tion as the rollers approach the ends of their travel or stroke on the guideway. This negative spring action produces longitudinal spring forces on the rollers near the ends of their travel in the direction toward these ends which urge the rollers to the ends; That is to say, as the rollers approach either end of the guideway, the band exerts an increasing force on the rollers which urges the cluster to the approached end. i

For a more detailed description of the ROLAMITE roller mechanism, references may be had to an industrial applications brief number SC-M-68-232A entitled Introduction to the ROLAMITE Mechanical Design Concept, published in September, 1968, by the Office of Industrial Cooperation, Sandia Laboratories, Albuquerque, N. Mex. Other Prior art references of interest are US. Pat. Nos. 2,934,938, 3,452,175, 3,452,309, 3,471,668 and 3,572,141.

SUMMARY OF THE INVENTION Generally speaking, the present invention provides a positive displacement fluid actuated device which may be combinedwith transducers and a readout unit to form a fluid flowmeter for measuring flow volume and flow rate. According to one aspect of the invention, the fluid actuated device is provided with a pair of cylinders each containing a pressure wall means which is movable through the cylinder by the pressure of the fluid flow being measured. The pressure wall means in each cylinder performs a valving function for directing fluid flow to the other cylinder in such a way that movement of each wall means to either end of its working stroke effects delivery of fluid to one end of the other cylinder for driving the corresponding wall means from one end of its working stroke to the other. The pressure wall means are thus driven back and forth through their working strokes in alternating fashion.-

The cylinders are provided with transducers for sensing and generating signals representing the positions of the wall means along and/or the velocity of the wall means through their cylinders. These signals are fed to a readout unit which provides a readout representing flow rate and/or flow volume, as the'case may be.

Anotheraspect of the invention is concerned with the utilization of a ROLAMITE roller mechanism as a positive displacement fluid actuated flow metering device for use in the flowmeter. This fluid actuated device has a roller and band assembly similar to that of a conventional ROLAMITE mechanism contained within and disposed in fluid sealing relation to the inner surfaces of a rectangular cylinder in such a way that the roller cluster forms a movable pressure wall in the cylinder. Valve means are provided for admitting the fluid to be measured to and venting the cylinder ends alternately'in such a way that the roller cluster is driven back and forth through the cylinder by fluid flow. The

cylinder mounts a transducer for sensing the velocity and position of the roller cluster and generating signals proportional to these quantities which may be fed to the readout unit of the flowmeter to provide a readout of flow rate and/or flow volume.

According to a feature of the invention, the roller cluster velocity and position sensing transducer has an element which moves. relative to a stator to produce the roller velocity and/or position signals. This movable transducer element is operatively connected to the roller band in such a way that a given displacement of the roller cluster through the cylinder causes twice the displacement of the element, thus increasing the sensitivity and accuracy of measurement. According to another feature, the roller band may be notched or etched to provide a negative spring action as the roller cluster approaches each end of its travel or working stroke in the cylinder. This negative spring action produces spring forces on the roller cluster for urging it to the ends of its stroke.

Two of these fluid actuated ROLAMITE devices may be interconnected to operate in unison in the manner mentioned earlier. In this case, the rollers of each device perform the valving function for controlling fluid flow to the cylinder of the other device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a flowmeter according to the inventron;

FIG. 2 is an enlarged side view, partly broken away, of the present fluid actuated flow metering device embodied in the flowmeter;

FIG. 3 is a section taken on line 3-3 in FIG. 2;

FIG. 4 is a section taken on line 44 in FIG. 3;

FIG. 5 is a section taken on line 5-5 in FIG. 3;

FIG. 6 is a diagram illustrating the motion of certain rollers embodied in the flow metering device of FIGS. 2-5;

FIG. 7a is a diagrammatic view of ,a roller-wrapped configuration of a roller band embodied in the device;

FIG. 7b is an unwrapped plan view of the roller band of FIG 7a; and

FIG. 70 is a diagram illustrating cluster force .vs. displacement characteristics effected by the band of FIGS. 7a and 7b.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, the illustrated flowmeter l0 comprisestwo basic components 12 and 14. Component 12 is a positive displacement fluid actuated flow metering device according to the invention and component 14 is a readout unit. The fluid whose flow volume and/or flow rate is to be measured passes through the flow metering device 12 and actuates the latter in the manner described later. The device provides output signals proportional to the measured quantity or quantities. Thereadout unit 14 receives these signals and provides a readout representing each quantity.

Turning to FIGS. 2-7, the metering device 12 comprises a cylinder housing 16 having a central body member 18 comprising two generally hollow rectangular shapes, and inner and outer side plates 20 and 22 secured at each side of the body member by bolts 24.

Body member 18 has parallel equally spaced intervening wall members 30, 32, 34 extending between and integrally joined to end wall members 26, 28. The housing side plates 20, 22 close the open sides of the body member 18 to define between the wall members 30, 32 and 26, 28, a first cylinder 36, and between the wall members 32, 34 and 26, 28, a second cylinder 36. Each of these cylinders has a generally rectangular crosssection.

Contained within each cylinder 36 is a pressure wall means 40 which is movable longitudinally through the cylinder. These pressure wall means willbe described the left-hand port the outlet port. It will become evident as the description proceeds, however, that the direction of flow through the metering device may be reversed.

The fluid metering device 12 includes valve means 46 for communicating the ports 42, 44 to opposite ends of the cylinders 36 to effect movement of the pressure wall means 40 back and forth through working strokes in their cylinders by the fluid flow being measured. According to a feature of the invention, the valve means 46, or more correctly the valving function of the valve means, is controlled by the pressure wall means 40 in such a way that the flow of fluid to and from each cylinder 36 is controlled by the wall means in theother cylinder. More specifically, movement of each wall means to either end of its working stroke conditions the valve means to deliver fluid to an end of the cylinder for the other wall means and vent the opposite end of the latter cylinder and whereby effectdriving of the latter wall means from one end to the other end of its working stroke by fluid flow. Accordingly, the pressure wall means are driven back and forth through their workin strokes in alternate fashion.

Movement of each pressure wall means 40 through each working stroke represents flow into one end of the respective cylinder 36 of a fluid volume equal to the displacement volume of the stroke and flow of an equal fluid volume from the opposite end of the cylinder. Accordingly, the total number of strokes of the two pressure wall means over a given measurement period is proportional to the total flow volume of fluid which passes through flow metering-device 12 during the period. Thus, the velocity of the wall means moving through their working strokes is proportional to the existing flow rate.

Mounted on the cylinder housing 16 are transducer means 48 for sensing the positions of the pressure wall means 40 in their respective, cylinders 36 and the velocities of the wall means through their working strokes in the respective cylinders. Transducer means 48 generate electrical signals representing the positions and velocities of the respective wall means. The readout unit 14 receives these signals and converts the latter to readouts representing flow volume and flow rate.

As noted earlier, each of the illustrated pressure wall means 40 comprises a roller and band assembly similar to that utilized in a ROLAMITE mechanism. Thus,

eachwall means comprises a pair of rollers of equal diameter 50, 52 entwined by a thin elastically flexible band 54. The rollers extend crosswise of the respective cylinder 36 and have their end faces disposed in fluid sealing relation to the inner surfaces of the inner cylinder housing side plates 20.

Referring to FIG. 3, improved and excellent sealing between the roller end surfaces and the side plates may preferably be provided by dividing or splitting each roller into two parts, as indicated at 51, and utilizing helical springs 53 and guide pin 55 to effect light resilient urging of the roller end surfaces against the side plates. Frictional losses'between the roller end surfaces and the side plates may be minimized by reducing the areas of contact, preferably by slightly indenting or recessing 7 surfaces are referred to as guide surfaces and, for this reason, are so referred to in this description. The axes of rollers 50, 52 are offset both longitudinally and laterally relative to the cylinder 36 and are restrained by band 54 in such manner that the plane containing the axes of the two rollers is disposed at an acute angle, known as the angle of repose, relative to the guide surfaces.

The roller band 54 has a width slightly less than the length of the rollers 50, 52. One end of the band in the upper cylinder is attached by fasteners 60 to the upper guide surface 56 adjacent the cylinder housing end wall 28. The band extends from this end wall along and in contact with the guide surface 56, then between the latter and roller 50, then around the latter roller 50 and between it and roller 52, then around roller 52 and between it and the lower guide-surface 58, and finally along and in contact with the latter guide surface toward the cylinder housing end wall 26. The end of the band is attached by fasteners 60 to the lower guide surface adjacent to end wall 26. The band 54 is tensioned lengthwise in such a way that the rollers 50, 52 are captivated by the band and retained at the illustrated angle of repose. As is well known to those familiar with the ROLAMITE mechanism, th'e rollers 50, 52 are movable back and forthwith a virtually frictionless motion involving pure rolling contact between the rollers and the band 54.The roller and band arrangement in the lower cylinder is virtually identical to that in the upper cylinder except that the positions of the rollers 50, 52 are reversed.

The two rollers 50, 52 in each cylinder 36 and the arcuate portion of the band 54 entwining the rollers is re ferred to as a roller cluster, or simply cluster. These roller clusters form the pressure wall means 40 of the fluid metering device 12 and hence are referred to by' the same reference numeral.

The cylinder housing side plates 20, a contain manifold passages 62 for communicating the inlet and outlet ports 42, 44 to the ends of the cylinders 36. As will be explained presently, fluid flow through these passages is controlled by the valve means 46 whose valving function, in turn, is controlled by the cylinder rollers 50, 52. Passages 62 are formed by grooves in the outer surfaces of the inner cylinder housing side plates 20, 20a, and closed by the outer side plates 22, 22a. Each side plate 20, 20a contains a set of fluid passages. The two sets of passages are mirror images of each other and are interconnected by inlet and outlet passages extending through the center cylinder housing wall 32 and communicating with the inlet and outlet ports 42, 44 in plate 22.

Referring particularly to H65. 3 and 4, it will be observed that the fluid passages 62 in the side plates 20, 20a include ports which'open to the cylinders 36. In the ensuing description, the ports which open to the upper cylinder are designated by a numeral and an upper case letter, i.e., 68A. The ports which open to the lower cylinder are designated by a numeral and a lower case letter, i.e., 68a. The corresponding ports for the two cylinders' are designated by the same numeral and letter.

The ports which open to the uppercylinder 36 include a first group of three ports 68A, 68B, 68C and a second group of three ports 70A, 70B, 70C whose exact location will be explained presently. Suffice it to say at this point that the three ports in each group are uniformly spaced and located approximately in a common transverse plane of the upper cylinder. The two transverse planes containing the port groups are approximately equally spaced from one another and from the cylinder housing end walls 26, 28. Opening to the left and right ends of the upper cylinder are ports 72A,

The lower cylinder 36 has essentially the same port arrangement as the upper cylinder except that the lower port arrangement is reversed endwise of the cylinder relative to the upper port arrangement. Accordingly, it is unnecessary to describe the lower port arrangement. As noted earlier, the lower ports are designated by the same numerals and letters as their corresponding upper ports except that the designating letters for the lower ports are lower case letters.

The upper cylinder ports 68A, 70A and lower cylinder port 72a are connected by a passage 76. Similarly, the lower cylinder ports 68a, 70a and upper cylinder port 72Aare connected by a passage 78. Cylinder ports 68B, 7012 and outlet port 44 are connected by a passage 80. Similarly, cylinder ports 70B, 68b and inlet port 42 are connected by a passage 82. Finally, a passage 84 connects the cylinder ports 68C, 70C, 740, and a passage 86 connects ports 68c, 70c, 74A.

As noted earlier, the rollers 50, 52-perform a valving function. To this end, each end face of each roller 50 has a pair of cavities 88, 90 angularly spaced about the roller axis. Similarly, each end face of each roller52 has a pair of angularly spaced cavities 92, 94. FIG. 6

depicts the paths followed by these roller cavities as a roller moves through its working stroke, and specifically represents the kinematics of roller 52 of upper cylinder 36 relative to ports 68A, 68B and 68C.

. The above described cylinder ports and cavities are arranged and oriented to accomplish the following operating cycle when the inlet port 42 is connected to a supply of fluid flowing from a fluid system under pres sure and outlet port 44 is connected to a lower pressure region of the fluid system. Assume that the upper roller cluster pressure wall means 40 is initially at the right end of its working stroke, as in FIG. 4. Cavities 88 in the upper roller 50 then register with the upper cylinder ports 70A, 70B and cavities 92 in the upper roller 52 register with the upper cylinder ports 68B, 68C.

Under these conditions, fluid flow occurs from inlet port 42, through passages 32, 76 to the right end of the lower cylinder 36, and from the left end of the lower cylinder, through passages 84, 80 to the outlet port 44. Accordingly, the lower roller cluster 40 is driven to the left end of its working stroke by the fluid flowing under pressure into the right end of the lower cylinder.

When the lower roller cluster 40 is located at the left end of its working stroke, the cavities 88 in the lower roller 50 register with the lower cylinder ports 70a, 70b, and the cavities 92 in the lower roller 52 register with the lower cylinder ports 68b, 68c. Fluid flow thenoccurs from the fluid inlet 42, through passages 82, 86 to the right end of the upper cylinder 36, and from the left end of the upper cylinder through passages 78, 80 to the outlet port 44. Accordingly, the ,upper roller cluster 40 is driven to the left end of its working stroke by the fluid flowing under pressure into the right end of the upper cylinder.

' Arrival of the upper rollercluster 40 at the left end of its working stroke registers the cavities 90 in the upper roller 50 with the upper cylinder ports 78B, 78C

and the cavities 94 in the upper roller 52 with the upper cylinder ports 68A, 68B. Fluid flow then occurs from the fluid inlet 42, through passages 82,84 to the left end of the lower cylinder 36, and from the right end of the lower cylinder through passages 76. 80 to the outlet port 44. The fluid flowing under pressure into the left end of the lower cylinder now drives the lower roller cluster to the right end of its workingstroke.

When the lower roller cluster reaches the right end of its stroke, the cavities 94 in the lower roller 52 regisfluid metering device 12 and to commence the next cycle.

It will now be understood that the rollers 50, 52 of the fluid metering device 12 perform a valving function in combination with their cylinder ports in such a way that the rollers in each cylinder control the fluid flow to the other cylinder to effect driving of the upper and lower roller clusters forming pressure wall means 40 through their working strokes in alternating sequence.

' According to a feature of the invention, the roller band 54 may be reduced in thickness or notched, as by chemical etching, to provide the clusters with a negative spring action as their rollers approach end of their working strokes, .thus to urge the clustersto the approached stroke end. For example, FIG. 7b shows a band, in its normal flat configuration, which has been etched to a depth of one-half of its thickness in the areas indicated by cross-hatching. FIG. 7a shows in side elevation this band wrapped about rollers with the cluster atfull left-hand position. FIG. 70 depicts the characteristics of the cluster force vs. displacement over thefull stroke of the cluster. The actual mechanics of such negative spring action are known in the art, and are described, for instance, in the earlier referenced ROLA- MlTE publication and hence need not be elaborated on further. v

in actual flow measurement use, metering device 12 is connected to a-fluid system which conveys the fluid to be measured in such a manner that the measured fluid actuates the device. it is apparent at this point that the number of working strokes executed by the two roller clusters within their respectivecylinders 36 during a given time period of flow measurement is proportional to the total flow volume during that time period, and that the sum of the velocities of the two roller clusters is proportional to the flow rate.

As noted earlier, the transducer means 48 produce output signals representing the positions and velocities of the roller clusters which form the pressure wall means 40 in their respective cylinders. Transducer means 48 comprise a pair of separate transducers 96 mounted on the cylinder housing end wall 28 opposite the cylinders 36, respectively, for sensing the position and velocity of the respective roller clusters 40. A variety of transducers may be used for this purpose. The particular transducers 96 shown are commercially available transducers, each of which has a pressuresealed barrel 98 securedat one end to the end wall 28 and a plunger'or probe 100 movable in the barrel. The barrel 98 contains a coil (not shown) and the plunger 100 has a permanent magnetic core (not shown) movable through the coil. Movement of the core through the coil generates a voltage in the coil proportional to the linear velocity of the core. The transducer also includes electricalcontact means, such as conduction sections on the plunger and barrel which close or engage at predetermined positions of travel of the plunger in the barrel.

The plunger 100 of each transducer 96 extends through the end wall 28 into the adjacent cylinder 36. The extending end of each plunger is attached to a midpoint of the respective roller band 54 by a flexible tongue 102 which slidably engages a tongue guide 104 secured to surface 56, so that the movement of the band occasioned by movement of the roller cluster 40 back and forth in the cylinder causes movement of the plunger through its barrel. A unique feature of the invention in this regard resides in the fact that the travel and velocity of the plunger are approximately twice the travel and velocity of the roller cluster because the tongue velocity corresponds to the velocity of the uppermost point. of the adjacent roller. If necessary, the transducer may have a spring for urging the plunger to the left in its barrel during left-hand travel of the respective roller cluster. However, for usual operation;

- the normally flat tongue sliding on the tongue guide provides sufficient longitudinal strength to drive the plungerf It is now evident that during the earlier described operation of the fluid metering device 12 the transducers 96 generate output voltage proportional to the linear velocities of their roller clusters 40 through the cylinders. The position sensing contact means of the transducers are set to close as their roller clusters approach the ends of their strokes, thus providing signals repre- I senting successive strokes of the clusters, as well as providing information to the readout unit 14 as to the spe cific (right or left) stroke-end position of an individual cluster, as required for determining the flow direction into metering unit 12.

As noted earlier, the transducers 96 are connected to the readout unit 14. This readout unit includes an integrating circuit for integrating the velocity output signals from the transducers and providing a readout representing flow volume over a time period. The readout unit also includes a counter actuated by closure of the transducer position contacts for counting the strokes of the roller clusters 40 and providing a readout representing the count in terms of flow volume.

Fluid flow may occur in either direction through the fluid metering device 12, as already noted, and is evident from the earlier description of the device. The direction of flow through the device will result in the readout unit 14 providing the corresponding positive or negative flow volume and flow rate readings with appropriate sense indication.

The apparatus herein disclosed provides the following combined advantages over known devices available for flow measurements: l Positive-displacement principleof measurement; (2.) accurate measurement, using a single flowmeter configuration, over a very wide range of flow rate; (3)-self-calibrating feature, providing continual and automatic re-calibration of flow rate measurement as required. to compensate for time, temperature changes, and other parameters; (4) imperviousness to liquid pressure level; (5) usable with a wide variety of fluid. types; (6) excellent operation virtually unaffected by fluid viscosity contamination, and temperature, over wide range; (7) usable for dynamic (time-varying) as well as static flow rate measuring; (8) continuous bi-directional flow rate measurement and polarity .indication; (9) may utilize digital auto-ranging panel readout, and both digitally-coded and analog electrical signal availability for external controlling, indicating, or recording of flow rate; (10) total flow readout electrical analog signal availability; (11) flow rate measurement hold readout feature; l2) extremely low differential pressure drop from zero flow to the rated flow rate of the apparatus in either direction; (l3) virtually unlimited operating life ensured by design which encloses all moving parts for operation at the pressure level of the measured fluid, and excludes all high differential pressure moving seals.

' What is claimed as new in support of Letters Patent 1. A fluid flow actuated device comprising:

a pair of cylinders of rectangular cross-section each having longitudinal side walls and longitudinal guide walls normal to said side walls,

a pair of rollers within each cylinder having ends disposed in fluid sealing relation with said cylinder side walls, and diameters whose sum exceeds the spacing between said guide walls, and a flexible elastic band anchored at its ends to said guide walls, respectively, adjacent the cylinder ends and trained about said rollers in such a way that the rollers are caged by said band and movable in unison through the cylinder with pure rolling contact between the rollers and band, the roller pair in each cylinder and the corresponding elastic band constituting a pressure wall means movable through longitudinal working strokes in the cylinder,

means on said cylinders providing fluid inlet and outlet ports,

valve means controlled by the pressure wall means for selectively communicating said ports to the ends of said cylinders in a manner such that movement of the wall means of either cylinder to the end of its working stroke effects communication of said ports with the ends, respectively, of the other cylinder, whereby said wall means are driven back and forth through their working strokes alternately when said inlet port is supplied with fluid under pressure, and

transducer means connected to said pressure wall means for generating signals representing at least one of the variables (a) velocity of the pressure wall through each cylinder, and (b) the ends of said working strokes.

2. A fluid flow actuated device according to claim 1 including:

readout means connected to said transducer means for providing a readout representing flow rate and- /or total fluid flow passing through the device. 3. A fluid flow actuated device according to claim 1 wherein:

said transducer means comprise a transducer for each cylinder for generating said signals, each transducer comprising a pressure-sealed barrel secured to one end of the respective cylinder, a plunger movable in the barrel, and a flexible tongue secured at one end to said plunger and at the opposite end to the respective flexible band.- 4. A fluid actuated device according to claim 1 wherein:

said valve means comprise valve ports opening I through the inner surfaceof at least one side wall of each cylinder, fluid passages communicating said valve ports for each cylinder to the ends of the other cylinder and to said inlet and outlet ports in a predetermined arrangement, and valve cavities in the ends of said rollers of each cylinder for communicating the respective cylinder valve ports in a predetermined relation when the rollers are at the ends of their working strokes.

5. A fluid actuated device according to claim 4 wherein:

the rollers of each cylinder have a first pair of valve cavities which communicate the ends of the other cylinder to said inlet and outlet ports at one end of the working stroke of the respective rollers and a second pair of valve cavities which communicate 'the ends of the other cylinder to said inlet and outlet ports in reversed order at the other end of the working stroke of the respective rollers.

6. A fluid flow actuated device according to claim 1 wherein:

said elastic band of each pressure wall means has an area of reduced thickness to provide a negative spring constant characteristic near the end of the working stroke of the respective rollers such that increasing force is exerted on said rollers as the latter approach each stroke end and in a direction to urge the rollers toward the respective stroke end.

7. A fluid actuated device according to claim 6 including:

readout means connected to said transducer means for providing a readout representing each measured variable. 8. A fluid actuated device according to claim 6 wherein:

said transducer means comprises a transducer for each cylinder including a pressure-sealed barrel secured to one end of the respective cylinder, a plunger movable in the barrel, and a flexible tongue secured at one end to said plunger and at the opposite end to the respective flexible band. 9. In a fluid pressure actuated device, the combination comprising:

a cylinder of rectangular cross-section including parallel longitudinal side walls and parallel longitudinal guide walls normal to said side walls, pressure wall means movable through longitudinal working strokes in said'cylinder in fluid sealing relation to said cylinder walls including a pair of rollers within said cylinder having ends disposed in fluid sealing relation with 'said cylinder side walls, and diameters whose sum exceeds the spacing between said guide walls, and a flexible elastic band anchored at its ends to said guide walls, respectively, adjacent the cylinder ends and trained about said rollers in such a way that the rollers are caged by said band and movable in unison through the cylinder with pure rolling contact between the rollers and band, and

passage means providing fluid ports opening to the ends of said cylinder through which the cylinder ends may be alternately pressurized and vented to effect back and forth motion of said wall means through working strokes in said cylinder, and

transducer means connected to said pressure wall means for generating signals representing at least one of the variable (a) velocity of the pressure wall through said cylinder, and (b) the ends of said working strokes.

10. A fluid flow actuated device according to claim 9 including:

readout means connected to said transducer meansfor providing a readout representing each measured variable.

11. A fluid flow actuated device according to claim 9 wherein:

said transducer means comprises a transducer including a pressure-sealed barrel secured to one end of said cylinder, a plunger movable in the barrel, and a flexible tongue secured at one end to said plunger and at the opposite end to said flexible band. 12. A fluid flow actuated device according to claim 9 wherein: I

said elastic band of pressure wall means has an area of reduced thickness to provide a negative spring constant characteristic near the ends of the working stroke of said rollers such that increasing force is exerted on said rollers as the latter approach each stroke end and a direction to urge the rollers toward the respective stroke end. 

1. A fluid flow actuated device comprising: a pair of cylinders of rectangular cross-section each having longitudinal side walls and longitudinal guide walls normal to said side walls, a pair of rollers within each cylinder having ends disposed in fluid sealing relation with said cylinder side walls, and diameters whose sum exceeds the spacing between said guide walls, and a flexible elastic band anchored at its ends to said guide walls, respectively, adjacent the cylinder ends and trained about said rollers in such a way that the rollers are caged by said band and movable in unison through the cylinder with pure rolling contact between the rollers and band, the roller pair in each cylinder and the corresponding elastic band constituting a pressure wall means movable through longitudinal working strokes in the cylinder, means on said cylinders providing fluid inlet and outlet ports, valve means controlled by the pressure wall means for selectively communicating said ports to the ends of said cylinders in a manner such that movement of the wall means of either cylinder to the end of its working stroke effects communication of said ports with the ends, respectively, of the other cylinder, whereby said wall means are driven back and forth through their working strokes alternately when said inlet port is supplied with fluid under pressure, and transducer means connected to said pressure wall means for generating signals representing at least one of the variables (a) velocity of the pressure wall through each cylinder, and (b) the ends of said working strokes.
 2. A fluid flow actuated device according to claim 1 including: readout means connected to said transducer means for providing a readout representing flow rate and/or total fluid flow passing through the device.
 3. A fluid flow actuated device according to claim 1 wherein: said transducer means comprise a transducer for each cylinder for generating said signals, each transducer comprising a pressure-sealed barrel secured to one end of the respective cylinder, a plunger movable in the barrel, and a flexible tongue secured at one end to said plunger and at the opposite end to the respective flexible band.
 4. A fluid actuated device according to claim 1 wherein: said valve means comprise valve ports opening through the inner surface of at least one side wall of each cylinder, fluid passages communicating said valve ports for each cylinder to the ends of the other cylinder and to said inlet and outlet ports in a predetermined arrangement, and valve cavities in the ends of said rollers of each cylinder for communicating the respective cylinder valve ports in a predetermined relation when the rollers are at the ends of their working strokes.
 5. A fluid actuated device according to claim 4 wherein: the rollers of each cylinder have a first pair of valve cavities which communicate the ends of the other cylinder to said inlet and outlet ports at one end of the working stroke of the respective rollers and a second pair of valve cavities which communicate the ends of the other cylinder to said inlet and outlet ports in reversed order at the other end of the working stroke of the respective rollers.
 6. A fluid flow actuated device according to claim 1 wherein: said elastic band of each pressure wall means has an area of reduced thickness to provide a negative spring constant characteristic near the end of the working stroke of the respective rollers such that increasing force is exerted on said rollers as the latter approach each stroke end and in a direction to urge the rollers toward the respective stroke end.
 7. A fluid actuated device according to claim 6 including: readout means connected to said transducer means for providing a readout representing each measured variable.
 8. A fluid actuated device according to claim 6 wherein: said transducer means comprises a transducer for each cylinder including a pressure-sealed barrel secured to one end of the respective cylinder, a plunger movable in the barrel, and a flexible tongue secured at one end to said plunger and at the opposite end to the respective flexible band.
 9. In a fluid pressure actuated device, the combination comprising: a cylinder of rectangular cross-section including parallel longitudinal side walls and parallel longitudinal guide walls normal to said side walls, pressure wall means movable through longitudinal working strokes in said cylinder in fluid sealing relation to said cylinder walls including a pair of rollers within said cylinder having ends disposed in fluid sealing relation with said cylinder side walls, and diameters whose sum exceeds the spacing between said guide walls, and a flexible elastic band anchored at its ends to said guide walls, respectively, adjacent the cylinder ends and trained about said rollers in such a way that the rollers are caged by said band and movable in unison through the cylinder with pure rolling contact between the rollers and band, and passage means providing fluid ports opening to the ends of said cylinder through which the cylinder ends may be alternately pressurized and vented to effect back and forth motion of said wall means through working strokes in said cylinder, and transducer means connected to said pressure wall means for generating signals representing at least one of the variable (a) velocity of the pressure wall through said cylinder, and (b) the ends of said working strokes.
 10. A fluid flow actuated device according to clAim 9 including: readout means connected to said transducer means for providing a readout representing each measured variable.
 11. A fluid flow actuated device according to claim 9 wherein: said transducer means comprises a transducer including a pressure-sealed barrel secured to one end of said cylinder, a plunger movable in the barrel, and a flexible tongue secured at one end to said plunger and at the opposite end to said flexible band.
 12. A fluid flow actuated device according to claim 9 wherein: said elastic band of pressure wall means has an area of reduced thickness to provide a negative spring constant characteristic near the ends of the working stroke of said rollers such that increasing force is exerted on said rollers as the latter approaches each stroke end and a direction to urge the rollers toward the respective stroke end. 